Typically, it is necessary, when producing oil and/or gas from an unconsolidated subterranean formation, to prevent sand grains and/or other formation fines from migrating into the wellbore and being produced from the well. The production of such particulates can reduce the rate of hydrocarbon production from the well and can cause serious damage to well tubulars and to well surface equipment.
Gravel packs are often used to control particulate migration in such producing formations. A gravel pack typically consists of a mass of particulates which are packed around the exterior of a screening device. Such screening devices, typically positioned in an open hole or inside the well casing, have very narrow openings which are large enough to permit the flow of formation fluid but small enough to allow the particulates to pass through. The particulates operate to trap, and thus prevent the further migration of, formation sand and fines which would otherwise be produced along with the formation fluid.
In order to be useful in gravel packing applications, such particulates must exhibit high strength and be capable of functioning in low permeability formations. Ultra lightweight (ULW) particulate materials have been proposed for use in gravel packing applications to improve transport, placement, and packing efficiency. Concerns exist however that ULW particulate materials do not demonstrate the acid and chemical resistance properties required of particulates for use in gravel packing.
U.S. Pat. No. 5,531,274 reports the use of polystyrene divinylbenzene (PSDVB) beads for use in hydraulic fracturing at temperatures up to about 150° F. PSDVB beads have been reported to reduce fluid velocity required to maintain proppant transport within the fracture. This, in turn, provides for a greater fracture area to be propped. When used as a proppant, PSDVB beads, while offering excellent compressive strength, often soften and loose their compressive strength especially at high temperature and high pressure conditions.
While PSDVB beads have sufficient strength, acid resistance and low ASG for use as ULW in gravel packing treatments, they are unfortunately subject to fluidization and flowback and thus are unacceptable for such use.
Alternative ULW materials of low ASG which exhibit high particle strength, acid resistance and which are not subject to fluidization and flowback have been sought to improve transport, placement and packing efficiency.